Field of the Invention
Embodiments of the present invention relate to a turbocharger.
Description of the Related Art
A turbocharger is employed, for example, in an internal combustion engine mounted in a vehicle. In the conventional turbocharger, the energy of the exhaust gas of the internal combustion engine is recovered by a turbine. An impeller (compressor) connected to the turbine by a shaft is rotated by the recovered energy. Intake air is supercharged to the internal combustion engine by the rotating impeller. This helps to enhance the intake efficiency and to achieve an improvement in terms of output and fuel efficiency.
A flow path for the exhaust gas is formed in a turbine housing accommodating the turbine. An exhaust gas at a very high temperature (e.g., 800° C. or more) directly contacts the turbine housing. Thus, the turbine housing requires a very high heat resistance. Forming the turbine housing by using a material having a very high heat resistance will result in an increase in the cost of the turbine housing. Forming the turbine housing by using a material having a lower heat resistance and enhancing the cooling capacity of the turbine housing will result in an increase in loss of the energy of the exhaust gas. This will result in the deterioration of intake efficiency, which means this structure is rather undesirable.
Japanese Laid-Open Patent Publication No. 2011-247189 discloses a variable capacity type supercharger having a variable valve. The supercharger has a bearing housing adjacent to the turbine housing. Between the bearing housing and the turbine, there is provided a heat shield plate configured to shield the heat of the exhaust gas supplied to the bearing housing.
Japanese Laid-Open Utility Model Publication No. 61-192519 discloses a variable turbine nozzle type supercharger having a variable valve. The supercharger has a scroll chamber for guiding the exhaust gas to the turbine, and a bearing housing adjacent to the turbine housing. Between the scroll chamber and the bearing housing, there is provided a heat shield plate configured to shield the heat of the exhaust gas supplied to the bearing housing.
Japanese Laid-Open Patent Publication No. 2000-257436 discloses a turbine housing for use in a turbocharger which has a variable valve. The turbine housing has an inner end surface in close proximity to a movable vane corresponding to a variable valve. The inner end surface is formed through casting of a heat-resisting material which is very resistant to oxidation.
Japanese Laid-Open Utility Model Publication No. 63-183432 discloses a turbine housing for a supercharger that does not have a variable valve. A bearing housing is adjacent to the turbine housing. Between the bearing housing and the turbine, and between the bearing housing and a scroll chamber, there are provided heat shield plates configured to shield the heat of exhaust gas supplied to the bearing housing.
The turbine housings disclosed in Japanese Laid-Open Patent Publication No. 2011-247189, Japanese Laid-Open Utility Model Publication No. 61-192519, and Japanese Laid-Open Patent Publication No. 2000-257436 have a flow path through which the inflow exhaust gas flows until it reaches the turbine. In this route, no heat shielding is created. Thus, to further suppress the energy loss of the exhaust gas, it is necessary for the turbine housing to be formed of a material having a very high heat resistance.
In the prior-art techniques disclosed in Japanese Laid-Open Patent Publication No. 2011-247189 and Japanese Laid-Open Utility Model Publication No. 61-192519, there is newly provided a dedicated heat shield plate for shielding the heat supplied to the bearing housing. As a result, an increase in the number of components is involved.
In the prior-art technique disclosed in Japanese Laid-Open Utility Model Publication No. 63-183432, there are newly provided heat shield plates for shielding heat between the turbine and the bearing housing, and between the scroll chamber and the bearing housing. As a result, an increase in the number of components is involved.
The turbine housing has an inner wall of the flow path through which the inflow exhaust gas flows until it reaches the turbine, and a scroll member covering the inner wall. No particular description regarding the heat resistance of the scroll member is to be found in the document.
The turbocharger with the variable valve has a turbine housing. There is a need in the art for a turbocharger having a turbine housing formed of a lower heat resistance and configured to suppress the energy loss of the inflow fluid.